Open-Loop Vertical Drywell Gradient Correction System and Method

ABSTRACT

A system and method are disclosed for controlling a drywell including a receiver having upper and lower ends with the lower end being more insulated than the upper and having a temperature sensor in thermal contact therewith. Upper and lower heaters are in thermal contact with the upper and lower ends respectively. A controller includes an integrated circuit having a temperature sensor. A reading from the integrated circuit is used to control power to the upper heater and reduce a temperature gradient between the upper and lower ends of the receiver.

TECHNICAL FIELD

This invention relates to systems and methods for controlling drywelltemperature.

BACKGROUND OF THE INVENTION

It is typical for thermometers and thermal switches to be calibratedusing a drywell. Drywells may include a receiver in which a thermometeror thermal switch is inserted. A heating element and temperature sensorare in thermal contact with the receiver such that the temperaturewithin the receiver may be accurately set. The set temperature of thedrywell may then be compared to the readout temperature of thethermometer or the switching temperature of a thermal switch todetermine its accuracy. In some uses, a reference thermometer isinserted within the receiver along with the thermometer or switch beingcalibrated, and the readout of the reference thermometer is used forcalibration purposes.

It is important in some applications to provide a uniform temperaturegradient between the top and the bottom of the receiver such that thetemperature actually imposed on the probe is very close to the settemperature of the drywell or the readout temperature of the referencethermometer. In prior systems, two heating elements are used, one nearthe top of the receiver and another near the bottom. Two temperaturesensors also located near the top and the bottom of the receiver providefeedback. A controller receives signals from the temperature sensors anddrives the heaters such that the temperature sensors indicate the sametemperature.

The above described approach is costly inasmuch as it requires twothermal sensors. The sensors used must be of extremely high quality andsensitivity inasmuch as they are used for calibration of thermometersand thermal switches that are themselves highly accurate. The sensorsmay need to be accurate over a broad range—from about 20 to over 600degrees Celsius. Due to the large temperature changes to which thesensors are subject and the need for accuracy, each of the sensors mayneed to be serviced or replaced during the life of the drywell. Theadditional sensor further increases expense by requiring additionalcircuitry and processing power to provide feedback control using theoutput of the sensor.

In view of the foregoing it would be an advancement in the art toprovide a drywell using a single receiver mounted thermal sensor withoutincreasing the cost or processing requirements of the drywell.

SUMMARY OF THE INVENTION

In one aspect of the invention a drywell includes a receiver into whichthe probe of a thermometer or thermal switch may be inserted. Thereceiver has upper and lower ends, with the upper end being exposed toambient air and the lower end being substantially more insulated thanthe upper end. An upper heating element is in thermal contact with theupper end and a lower heating element is in thermal contact with thelower end. A temperature sensor is also in thermal contact with thelower end. The only temperature sensors providing an output regardingthe temperature of the receiver are positioned within the insulatedlower end. In an alternative embodiment, the only temperature sensor islocated proximate the upper end.

A controller is coupled to the heating elements and the temperaturesensor to control the temperature of the receiver. The controller mayinclude a printed circuit board having an ambient temperature sensormounted thereon. The ambient sensor may be embedded within an integratedcircuit mounted to the printed circuit board. In one embodiment, theintegrated circuit is a dual mode circuit having operational and sensingmodes. The controller may switch the integrated circuit into the sensingmode in order to measure the ambient temperature.

The controller is programmed to monitor the receiver temperature,compare the receiver temperature to a set temperature, and to calculatea lower heater power value effective to drive the receiver temperaturetoward the set temperate. The controller also calculates an upper heaterpower value according to the ambient temperature reading and at leastone of the set temperature and the receiver temperature. The upperheater value is effective to drive the temperature of the upper end ofthe receiver toward the set temperature and compensate for heat loss tothe ambient from the upper end. The controller then supplies the upperheater value and the lower heater value to the upper and lower heaters,respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of a drywell in accordance with anembodiment of the invention.

FIG. 2 is a side cross sectional view of a drywell in accordance with anembodiment of the present invention.

FIG. 3 is a schematic block diagram of a drywell in accordance with anembodiment of the present invention.

FIG. 4 is a process flow diagram of an open loop vertical gradientcorrection method in accordance with an embodiment of the presentinvention.

FIG. 5 is a process flow diagram of an alternative embodiment of an openloop vertical gradient correction method in accordance with anembodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIG. 1, a drywell 10 may include a housing 12. A vent plate14 may be secured near the top of the housing 12 and permit air to flowout of the drywell 10. The vent plate 14 defines an aperture 16positioned over a receiver 18. The receiver 18 includes one or moreapertures 20 sized to receive the probe 22 of a thermometer, thermalswitch, or the like. In use, the temperature of the receiver 18 iselevated to a specified temperature in order to test the thermalresponse characteristics and accuracy of the device being tested. Aheating element in thermal contact with the receiver 18 may be used tocontrol the temperature of the receiver 18.

The drywell 10 may include a control module 24 secured thereto.Alternatively, the control module 24 is remote from the drywell 10 andcoupled to the drywell 10 by wires or other communication means. Thecontrol module 24 may include an interface 26 for interacting with thedrywell 10. The interface 26 may include a display 28, input buttons 30,and ports 32 for coupling thermometers, thermal switches, and the liketo the control module 24 for testing.

Referring to FIG. 2, the drywell 10 may include a circuit board 34mounted within the control module 24. The circuit board 34 may include aprocessor 36 for executing executable data and processing operationaldata. In some embodiments, other integrated circuits 38 mount to thecircuit board 34 and are in data communication with the processor 36. Inthe illustrated embodiment, one of the integrated circuits 38 is a dualmode analog to digital (A/D) converter, having operational andtemperature sensing modes.

The circuit board 34 may be exposed to ambient air flow 40, whetheractive or passive. For example, a fan may supply air to the circuitboard 34. Alternatively, the control module 24 may be supplied withvents permitting convective air flow therethrough. The circuit board 34may be separated from the receiver 18 by a wall 42. The wall 42 may beformed of metal, plastic, or other material. The wall 42 may includeinsulation thermally isolating the circuit board 34 from the receiver18.

The receiver 18 may include insulation 44 surrounding a lower end 46thereof. The insulation 44 may extend up to the upper end 48, butleaving the upper end 48 exposed in order to permit insertion of theprobe 22. Accordingly, the upper end 48 is subject to heat loss toambient air flow 50 to a much greater extent than the lower end 46.

A shield 52 may extend between the lower end 46 and the upper end 48 ofthe receiver 18. A fan 54 positioned below the receiver 18 may directairflow 56 between the insulation 44 and the shield 52. The fan 54 mayalso induce airflow 58 between the shield 52 and the housing 12.

As is apparent from FIG. 2, the circuit board 34 is thermally isolatedfrom the receiver 18 by means of the active cooling induced by the fan54, the shield 52, and the wall 42. Thermal isolation may advantageouslyreduce heat related variation in the functioning of the circuit boardand prevent damage.

A lower heating element 60 is secured in thermal contact with thereceiver 18 proximate the lower end 46. A temperature sensor 62, such asthermocouple or like sensor, may also be positioned in thermal contactwith the receiver 18 proximate the lower end 46. An upper heatingelement 64 may be secured in thermal contact with the receiver 18proximate the upper end 48.

The upper and lower heating elements 60, 64 may be controlled by thecircuit board 34. In some embodiments, intervening current handlingcircuits may be positioned electrically between the heating elements 60,64 and the circuit board 34 to supply actual current to the heatingelements 60, 64 subject to control signals from the circuit board 34.

Referring to FIG. 3, the control module 24 may include a feedbackcontrol module 66 in electrical communication with the temperaturesensor 62 and the lower heating element 60. The feedback control module66 may compare a reading from the temperature sensor 62 to a settemperature. The feedback control module 66 then determines an amount ofpower to supply to the lower heating element 60 in order to reach theset temperature.

The feedback control module 66 may communicate with a gradientcorrection module 68. The gradient correction module 68 determines froma measurement of ambient temperature a correction factor compensatingfor heat loss to the ambient. In the illustrated embodiment, thegradient control module 68 receives an input from the feedback controlmodule 66, such as a signal corresponding to one or more of the currentamount of power being supplied to the lower heating element 60, thecurrent set temperature, the current output of the temperature sensor,or some value derived from all or some of these factors. The feedbackcontrol circuit also receives a temperature measurement from theintegrated circuit 38 mounted to the circuit board 34. The gradientcorrection module 68 then calculates one or more correction factorsbased on the measurement from the integrated circuit 38 and the valuesreceived from the feedback control module 66.

In one embodiment, the gradient correction module 68 receives a valuecorresponding to the amount of power being supplied to the lower heatingelement 60 and either the set temperature or measured temperature. Thegradient correction module 68 may then add a correction factor to theamount of power being supplied to the lower heating element 60, multiplyit by a correction factor, or both to determine a corrected power value.The gradient correction module 68 then drives the upper heating element64 according to the corrected power value. In some embodiments, thetemperature measurement of the integrated circuit 38 is supplied to thefeedback control module 66 in order to determine the amount of power tosupply to the lower heating element 60.

The feedback control module 66 and gradient correction module 68 may beimplemented as digital or analog circuits or as code executed by aprocessor or by some other means. The components performing the functioncorresponding to these modules 66, 68 may be in the same or differentphysical or logical locations. The functions attributed the modules 66,68 may be performed by the same component simultaneously ornon-simultaneously.

Referring to FIG. 4, a method 70 for controlling a drywell 10 mayinclude measuring the temperature of the receiver 18 proximate the lowerend 46 at block 72. Block 72 may include measuring the temperature of abody in thermal contact with the receiver 18. At block 74 a settemperature and the temperature measured at block 72 are compared. Atblock 76 the amount of power to be supplied to the lower heater 60 iscalculated based on the comparison at block 74. The power may becalculated as a voltage, current, or a unit of energy such as watts. Theamount of power to be supplied may correspond to the difference betweenthe measured and set temperatures according to known principles ofcontrol dynamics.

At block 78, the ambient temperature is measured. At block 80, one ormore correction factors are calculated. The correction factors may beused to calculate the power to the upper heater 64. For example, thecorrection factors may be multiplied by, or added, to or otherwisecombined with the power value calculated at block 76 for the lowerheater 60 such that the temperature gradient between the upper end 48and lower end 46 due to heat loss to the ambient will be reduced.

At block 82, the amount of power to be supplied to the upper heater 64is calculated. Block 82 may include combining the correction factor withthe value calculated at block 76 or by calculating a power valueaccording to the temperature measured at block 78 and one or both of theset temperature and the temperature measured by the temperature sensor62. The upper power value is preferably effective to substantiallyreduce the temperature gradient between the upper and lower ends 48, 46caused by heat loss to the ambient.

At block 84, the power value calculated at block 76 is supplied to thelower heater 60 and at block 86, the power value calculated at block 82is supplied to the upper heater 64. The method 70 may repeatperiodically or substantially continuously.

Referring to FIG. 5, in an alternative embodiment, the step of measuringambient temperature at block 78 may be replaced by the illustratedsteps. At block 88, the temperature of the controller is measured. Thismay include measuring the temperature of the circuit board 34 comprisingthe control module 24, for example, the integrated circuit 38 mayinclude a temperature sensor providing a reading of the temperature ofthe integrated circuit 38. Inasmuch as the circuit board 34 is exposedto the ambient airflow 40, the temperature of the circuit board 34 andthe integrated circuit 38 at steady state will be reflective of theambient temperature. In some embodiments, block 88 may include switchingthe integrated circuit 38 from an operational mode, such as functioningas an A/D converter, to a sensing mode at block 90. The output of theintegrated circuit 38 is read at block 92. Block 88 may also includeswitching the integrated circuit back to the operational mode at block94.

Although the present invention has been described with reference to thedisclosed embodiments, persons skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention. Such modifications are well within the skillof those ordinarily skilled in the art. Accordingly, the invention isnot limited except as by the appended claims.

1. A drywell comprising: a receiver having first and second ends, one ofthe first and second ends being exposed to ambient air and defining anopening therein for receiving a probe and the other of the first andsecond ends being relatively more insulated from the ambient air; afirst heating element in thermal contact with the receiver proximate thefirst end and a second heating element in thermal contact with thereceiver proximate the second end; a receiver sensor in thermal contactwith the receiver proximate the second end, the receiver sensor beingthe only temperature sensor in thermal contact with the receiver; anambient sensor generating an ambient sensor reading; and a controller,the first and second heating elements, receiver sensor, and an ambientsensor in data communication with the controller, the controller beingprogrammed to monitor a temperature indicated by the receiver sensor, tocompare the temperature indicated by the receiver sensor to a settemperature, to calculate a first heater power value according to thecomparison, and to calculate a second heater power value according tothe ambient sensor reading and the temperature indicated by the receiversensor, the controller further programmed to power the first heateraccording to the first heater power value and power the second heateraccording to the second heater power value.
 2. The drywell of claim 1,wherein the controller is programmed to calculate the first and secondheater power values effective to reduce a temperature difference betweenthe first and second ends.
 3. The drywell of claim 1, wherein the secondend is relatively more insulated from the ambient air than the first endand wherein the first end is exposed to the ambient air.
 4. The drywellof claim 1, wherein the controller is programmed to calculate the firstheater power value by applying a correction factor to the second heaterpower value, the correction factor corresponding to the ambienttemperature reading.
 5. The drywell of claim 1, wherein the controlleris programmed to multiply the first heater power value by a correctionfactor to calculate the second heater power value.
 6. The drywell ofclaim 5, wherein the controller is programmed to add the correctionfactor to the first heater power value to calculate the second heaterpower value.
 7. A drywell comprising: a receiver having first and secondends, the first end being exposed to ambient air and defining an openingtherein for receiving a probe, the second end being relatively moreinsulated from the ambient air than the first end; a first heatingelement in thermal contact with the receiver proximate the first end anda second heating element in thermal contact with the receiver proximatethe second end; a receiver sensor in thermal contact with the receiverproximate the second end, the receiver sensor being the only temperaturesensor in thermal contact with the receiver; and a printed circuit boardcomprising a controller and an ambient sensor generating an ambienttemperature reading, the ambient sensor being embedded in an integratedcircuit mounted to the printed circuit board, the first and secondheating elements, receiver sensor, and an ambient sensor in datacommunication with the controller, the ambient sensor producing anambient temperature reading, the controller being programmed to monitorthe temperature indicated by the receiver, to compare the temperatureindicated by the receiver to a set temperature, to calculate a firstheater power value based on the comparison, and to calculate a secondheater power value according to the ambient temperature reading and atleast one of the set temperature and the receiver temperature, thecontroller further programmed to power the first heater according to thefirst heater power value and power the second heater according to thesecond heater power value.
 8. The drywell of claim 7, wherein theintegrated circuit has an operational mode and a sensing mode andwherein the controller is programmed to switch the integrated circuitinto the sensing mode to generate the ambient temperature reading. 9.The drywell of claim 8, wherein the integrated circuit includes ananalog to digital (A/D) converter.
 10. The drywell of claim 7, whereinthe controller is programmed to calculate the upper and lower heaterpower values effective to reduce a temperature difference between theupper and lower ends.
 11. The drywell of claim 7, wherein the controlleris programmed to calculate the second heater power value by applying acorrection factor to the first heater power value, the correction factorcorresponding to the ambient temperature reading.
 12. The drywell ofclaim 11, wherein the controller is programmed to multiply the firstheater power value by the correction factor to calculate the secondheater power value.
 13. The drywell of claim 6, wherein the controlleris programmed to add the correction factor to the lower heater powervalue to calculate the lower heater power value.
 14. The drywell ofclaim 11, wherein the controller is operably coupled to a memory storinga look-up table and wherein the controller is programmed to calculatethe correction factor according to the look-up table.
 15. The drywell ofclaim 14, wherein the look-up table maps correction factors to theambient temperature reading and at least one of the set temperature andreceiver temperature.
 16. The drywell of claim 7, further comprising ablower positioned to direct ambient airflow over the receiver.
 17. Thedrywell of claim 7, wherein the circuit board is thermally isolated fromthe receiver.
 18. A method for controlling a drywell comprising:measuring a receiver temperature proximate a lower end of a receiverhaving an upper end opposite the first end, the lower end beinginsulated and the upper end being uninsulated, the receiver having anupper heater in thermal contact with the receiver proximate the upperend and a lower heater in thermal contact with the receiver proximatethe lower end, a thermal sensor being in thermal contact with thereceiver proximate the upper end; comparing the receiver temperature toa set temperature; calculating a lower power value based on thecomparison that is substantially effective to drive the receivertemperature to the set temperature; measuring an ambient temperature;determining a heat loss gradient based on the receiver temperature andthe ambient temperature; powering the lower heater according to thelower power value; and powering the upper heater as a function of thetemperature gradient and the lower power value.
 19. A method forcontrolling a drywell comprising: measuring a receiver temperatureproximate a lower end of a receiver having an upper end opposite thefirst end, the lower end being insulated and the upper end beinguninsulated, the receiver having an upper heater in thermal contact withthe receiver proximate the upper end and a lower heater in thermalcontact with the receiver proximate the lower end, a thermal sensorbeing in thermal contact with the receiver proximate the upper end;comparing the receiver temperature to a set temperature; calculating alower power value based on the comparison that is substantiallyeffective to drive the receiver temperature to the set temperature;measuring an ambient temperature; calculating an upper power value basedon the ambient temperature and the receiver temperature; powering theupper heater according to the upper power value; and powering the lowerheater according to the lower power value.
 20. The method of claim 19,wherein measuring the ambient temperature comprises measuring a circuitboard temperature of a circuit board thermally isolated from thereceiver, the circuit board controlling power to the upper and lowerheating elements.
 21. The method of claim 20, wherein the circuit boardcomprises an integrated circuit having an operational mode and a sensingmode, and wherein measuring the circuit board temperature comprisesswitching the integrated circuit into the sensing mode to generate theambient temperature reading.
 22. The method of claim 21, wherein theintegrated circuit includes an analog to digital (A/D) converter. 23.The method of claim 20, wherein calculating the upper power valuecomprises applying a correction factor to the lower heater power value,the correction factor corresponding to the circuit board temperature.24. The method of claim 23, wherein applying a correction factor to thelower heater power value comprises multiplying the lower heater powervalue by the correction factor to calculate the upper heater powervalue.
 25. The method of claim 23, wherein applying a correction factorto the lower heater power value comprises adding the correction factorto the lower heater power value.
 26. The method of claim 23, whereinapplying the correction factor to the lower heater power value comprisescalculating the correction factor according to a look-up table.
 27. Themethod of claim 26, wherein the look-up table maps correction factors tothe ambient temperature reading and at least one of the set temperatureand receiver temperature.
 28. The method of claim 20, further comprisingdirecting ambient airflow over the circuit board and directing ambientairflow over the receiver.
 29. The method of claim 20, furthercomprising thermally isolating the receiver from the circuit board.